Control system for differential hydrostatic steering

ABSTRACT

A steering control system for a vehicle having a manual steering means such as a steering wheel and a dual path hydrostatic drive with separate motors for two steerable wheels, and separate variable output pumps for the motors in which a linkage interconnects the two motors. A pair of bars, preferably forming part of a parallelogram, controls and limits the movement of the linkage either in the same direction or in an angular direction to equalize the output of the motors or to vary the output of the motors to steer the vehicle. The movement of the interconnecting linkage is controlled by the steering means and the position of the two bars is preferably controlled by a foot pedal. Forward and reverse operation of the vehicle are obtained by shifting the linkage toward one or the other of the parallel members through the use of a resilient means, preferably a hydraulic motor. The present control system is particularly adapted for lift trucks in which the two front wheels are driven by the motors and a caster or casters are used for the rear wheels.

United States Patent [191 Williamson Jan. 1, 1974 CONTROL SYSTEM FORDIFFERENTIAL HYDROSTATIC STEERING [75] Inventor: William A. Williamson,Niles, Mich.

[73] Assignee: Clark Equipment Company,

Buchanan, Mich.

[22] Filed: Mar. 10, 1972 211 Appl. No.: 233,495

Primary Examiner-Leo Friaglia Assistant ExaminerJohn A. PekarAttorney-Marmaduke A. Hobbs et al.

SPEED CONTROL CLUTCH PEDAL 5 7 ABSTRACT A steering control system for avehicle having a manual steering means such as a steering wheel and adual path hydrostatic drive with separate motors for two steerablewheels, and separate variable output pumps for the motors in which alinkage interconnects the two motors. A pair of bars, preferably formingpart of a parallelogram, controls and limits the movement of the linkageeither in the same direction or in an angular direction to equalize theoutput of the motors or to vary the output of the motors to steer thevehicle. The movement of the interconnecting linkage is controlled bythe steering means and the position of the two bars is preferablycontrolled by a foot pedal. Forward and reverse operation of the vehicleare obtained by shifting the linkage toward one or the other of theparallel members through the use of a resilient means, preferably ahydraulic motor. The present control system is particularly adapted forlift trucks in which the two front wheels are driven by the motors and acaster or casters are used for the rear wheels.

12 Claims, 6 Drawing Figures I02 BIAS CYLINDER r, 104 7 88) I40? g {321:111"

32 SUPERCHARGE PUMP 50 4e 52 G ,72 64 5(8 66 P DIRECTIONAL CONTROL VALVEPATENTEU JAN 1 74 SPEED CONTROL CLUTCH PEDAL SHEET 1 OF 4 FIG. l

1oz BIAS CYLINDER DIRECTIONAL CONTROL VALVE 32 34\ 'SUPERCHARGE PUMP 5%{d P j 9 'PATENTEDJAN H914 3782.488

sum u 0F 4 "Fla-4 STE ER SLOT PARALLELOGRAM g\ 98\ :40 as |oo so W 82 JNEUTRAL STEER SLOT PIVOT CENTER Z- FORWARD SPEED IS O X 98 88 mo 82 TURNCONTROL SYSTEM FOR DIFFERENTIAL HYDROSTATIC STEERING The presentinvention relates to a mechanism or system for use with a vehicle havinga drive wheel on each side of the vehicledriven by a separate hydraulicmotor located at each wheel, the motors normally being driven byseparate variable displacement fluid pumps which are used, not only topropel, but to steer the vehicle. Most control systems in use today fallinto three general categories: namely, those controlled by two levers,those using a mechanism similar to bicycle handlebars in which theoperator holds the handlebars with both hands and pushes them forwardlyto travel forward and rotates the post on which the bars are mounted toturn the vehicle, and those having a T- handle which can be operatedwith one hand by the operator pushing the handle forward or back totravel and rotating it to turn the vehicle. All three of these types aredual path hydrostatic control systems which require special instruction,skills and practice to permit the operator to properly control thevehicle under all normal operating conditions.

Efforts have been made to adapt conventional automotive vehicle type ofcontrols to the foregoing systems, wherein a wheel is used to steer thevehicle; how ever, in the past a number of problems have beenencountered which rendered the wheel type systems impractical and/orunsafe. For example, if the system is arranged so that the operator hasnormal steering in the forward direction, he is likely to have reversesteering in the reverse direction, i.e. if he turns the wheel to theleft to turn left while going forward, he will steer to the right if heturns the wheel to the left while going in reverse. Further, since theturn radius is a function of vehicle speed, if the operator is goingstraight forward at a relatively high speed and turns the wheel slightlyhe will start a particular radius of turn, then while holding the wheelin that position and slowing the vehicle down, the turn radius willdecrease until the vehicle is stopped, at which point it is in centerpoint steering. Thus, the operation of the vehicle is unpredictable orat least difficult to predict, and hence unsafe to operate. It istherefore one of the principal objects of the present invention toprovide a steering and control system for dual path hydrostatic drives,in which the controls operate as a conventional automotive type having asteering wheel, a foot operated accelerating pedal and a control leverfor forward and reverse directions, and which has the inherent abilityto provide any type of steering response that may be desired under allnormal operating conditions.

The dual hydrostatic transmissions are of particular advantage in lifttrucks having a caster as the rear wheel, since they impart goodmaneuverability to the truck, including permitting turning on the centerpoint between the drive wheels. In this type of system in a lift truck,if the two drive wheels are driven at the same rate, the truck willtravel straight forward, and if one of the wheels is driven at adifferent rate of speed or in a different direction of rotation, thetruck will turn, the difference in wheel speeds determining the rate ofturn of the truck. The transmission systems on the trucks preferablyinclude variable displacement type pumps, hence the wheel speed, andthus the truck speed, can be varied independently of engine speed. It isa further object of the invention to provide a drive and steering systemfor use in lift trucks, which gives effective control of the truck whileutilizing maximum maneuverability of the hydrostatic system, and whichcan change the speed of the truck without affecting the turning radiusof the truck.

Still another object of the invention is to provide a control system ofthe aforesaid type for lift trucks which utilizes the operationalpattern of conventional automotive controls and which is capable ofmaintaining a constant steering rate regardless of the speed of thetruck, and when the truck is not moving, permitting turning of thesteering wheel without causing forward or rearward movement of thetruck.

Further objects and advantages of the present invention will becomeapparent from the following description and accompanying drawings,wherein:

FIG. 1 is a schematic diagram of the present control system fordifferential hydrostatic steering, showing the system in one operatingposition;

FIG. 2 is a plan view of the control system embodying a suitablemechanism for full control of a vehicle such as a lift truck, showingthe mechanism in neutral position;

FIG. 3 is a side elevational view of the operating mechanism shown inFIG. 1, together with a schematic diagram of a portion of the hydraulicsystem;

FIG. 4 is a diagram of the mechanism shown in FIGS. 1 and 2 showing themechanism in neutral position;

FIG. 5 is a diagram similar to that shown in FIG. 4, showing themechanism in position for driving the vehicle forwardly; and

FIG. 6 is a diagram similar to those shown in FIGS. 4 and 5,illustrating the position of the mechanism when the vehicle is beingturned to the right.

Referring more specifically to the drawings, the present mechanism isdesigned for use on a number of different types of vehicles, but it isparticularly adapted for use in connection with a dual hydrostaticsystem for lift trucks in which the two front wheels are driven byseparate motors, which are in turn driven by hydraulic pumps of thevariable capacity type. Various types of pumps and motors may be used inthe dual path system indicated generally by numeral 10 in FIG. 1, for alift truck having front wheels 12 and 14 driven by motors l6 and 18,respectively, the two motors being driven by variable displacement pumps20 and22, respectively. The pumps, in turn, are driven by the mainengine of the vehicle, which is indicated by numeral 24 in FIG. 3. Thetwo systems 28 and 30 of thee dual system 10 are identical inconstruction and operation, and hence like numerals will be given tolike parts in the two systems but distinguished by prime markings onone.

Motor 16 is driven by pump 20 in one direction by fluid through line 32and in the other direction by fluid through line 34, the pump being ofthe type which can be reversed to reverse the direction of motor 20. Inorder to maintain a predetermined minimum pressure in the lines so thatthe motor will be readily responsive to changes in the pump operation, asecondary hydraulic system indicated generally by numeral 40 suppliesfluid under pressure from pump 42 through lines 44, 46 and 48 to checkvalves 50 and 52. The maximum pressure in the line is controlled byrelief valve 54 in line fiwhich is connected to lines 32 and 34 by line58 having branches 60 and 62 in which are disposed check valves 64 and66. The relief valve is connected to return line 68 which returns thefluid to a sump 70 from which the pump receives the fluid formaintaining the aforementioned predetermined pressure limits in the dualsystem. A check valve 72 is provided in return line 74 to preventbackflow of fluid in the line to the pump when valve 54 relieves thepressure in the respective subsystem. The numerals used herein haveidentified the sub-system 28 and the same numerals with primes designatelike parts of the sub-system 30.

The pumps 20 and 22 which drive motors 16 and 18, respectively, includea swash plate controlled by rods 80 and 82 from mechanism generallyindicated by numeral 84. The rods, being movable inwardly and outwardlyof the pump body, vary the fluid displacement of pumps 20 and 22 byvarying the angular position of the swash plate. By controlling theposition of rods 80 and 82 through mechanism 84, the output of the twopumps is controlled either to maintain equal speed of motors 16 and 18,and hence obtain a straight forward or a straight rearward movement ofthe vehicle, or to obtain a differential in speed between the two motorsand thereby turn the vehicle either to the right or left, depending onwhich motor is'being driven at a greater speed.

The mechanism 84 includes a T-shaped member 88 having a stem 90pivotally connected to a shaft 92, and a pair of parallel plates form across arm 94 interconnecting rods 80 and 82 and connected to the end ofstem 90 opposite shaft 92, the ends of cross arm 94 having slots 96therein which engage a pair of pins 98 and 100 connected to control rods80 and 82, respectively. Shaft 92 is connected to the rod 102 of adoubleacting fluid motor 104 which includes a cylinder 106 and a piston108 slidably disposed within the cylinder and to which rod 102 isconnected. A pair of ports 110 and 1 12 communicate with the interior ofcylinder 106 at opposite ends thereof, and the fluid motor is supportedby a bracket 114 which is attached to a shaft 115 mounted for rotationin a trunnion 116 which is supported in a fixed position by bracket orframe member 1 17. The forward end of the T-member has a plate 118 whichrides or slides on an adjustable support means 1 19, and a sprocket 120is fixed to the upper end f a t 1121 11 1 .flqim e 104 may beam aboutshaft 11.6 between the position shown at 104 and the phantom outlineposition shown at 104'.

The ports 110 and 112 of fluid motor 104 are connected to a directioncontrol valve 122 which is supplied with pressurized fluid from a pump124 driven by vehicle engine 24. Valve 122 is operable so that fluid maybe selectively directed to either one of ports 110 and 112 or simplyreturned to the fluid reservoir 125. Further, a relief valve 123 isdisposed between pump 124 and valve 122 and is set at a relatively lowsetting so that the pressure fluid supplied to ports 1 l and 1 12 isonly about 25 psi. The fluid motor 104 acts as a liquid spring forbiasing member 88 in a direction toward or away from pumps 20 and 22 andchanges the output thereof accordingly.

Mechanism 84 includes a parallelogram linkage 130 which functions tolimit the movement of pins 98 and 100, and hence controls rods 80 and82. Linkage 130 includes a bar 132 and ,a bell crank 134 pivotallyconnected at 136 and 138, respectively. Connected in parallel relationbetween bar 132 and bell crank 134 are rods 140 and 142, and pins 98 and100 extend between the rods and are limited in movement thereby. Thebell crank 134 is connected by means of suitable linkage 143 to afoot-operated pedal 144 which operates parallelogram linkage 130 so thatrods 140 and 142 are moved toward each other in opposition to fluidmotor 104 operating through T-shaped member 88 and pins 98 and 100.Sprocket 120 is connected to another sprocket 146 by means of a chain148, and the latter sprocket in turn is connected to a steering wheel(not shown). By rotating the steering wheel and the sprocket and chainconnection, motor 104 is pivoted about shaft 115 between the extremepositions thereof shown in phantom. I

In the operation of the present system, with the mechanism disposed asshown in FIGS. 1, 2 and 4, the variable displacement pumps and 22 willbe at their neutral position, and hence the vehicle will not move, sinceneither pump is generating pressurized fluid. When the operatormanipulates valve 122 to select the forward direction, pressurized fluidis directed to port 110, thereby causing T-shaped member 88 to moveupwardly as viewed in FIG. 2, with pins 98 and 100 seating against rod140. Simultaneously, the operator controls the spacing between rods 140and 142 by depressing the foot pedal connected to linkage 130 so thatthe linkage is maintained in the position shown in FIGS. 1, 2 and 4.When the foot pedal is released, linkage 130 is actuated by spring 145,fluid motor 104 through the T-shaped member 88, and pins 98 and 100, tomove rods 140 and 142 away from each other, thereby allowing controlrods 80 and 82 to extend to the limit determined by the position ofpedal 144, since pins 98 and 100 follow in engagement with rod 140, inthat fluid motor 104 is exerting a bias on T-shaped member 88. Since thebias of fluid motor 104 is being supplied along a line parallel withrods 80 and 82, the two rods will move out together, with the resultthat the vehicle will be driven forwardly along a straight line. Inorder to drive the vehicle in a reverse direction, it is simplynecessary to actuate control valve 122 so that pressurized fluid isdirected to port 1 12, thereby biasing member 88 in the direction toengage pins 98 and 100 against rod 142.

To steer the vehicle, a differential in speed between wheels 12 and 14is created by moving the T-shaped member 88 to an angular position bymanipulating the steering mechanism. For example, the vehicle may besteered by slowing down the speed of the motor on the side of thevehicle in the direction toward which it is desired to turn the vehicle.If it is desired to turn the vehicle toward the right while it isproceeding forwardly, assuming that forward is toward the top of thedrawing as viewed in FIGS. 1, 2 and 6,-pump 22 will be operated so thatthe displacement thereof is decreased, thereby slowing down motor 18 andwheel 14 associated with the pump and motor.

If the vehicle is proceeding in a straight line in a forward direction,member 88 is biased toward the top of the drawing and linkage 130 hasbeen actuated so that bar 140 has been moved toward the top of thedrawing, with the result that rods 80 and 82 are extending out of thebodies of the respective pumps 20 and 22. When making a left turn, thesteering control wheel is actuated so that fluid motor 104 is pivoted ina counterclockwise direction about shaft l15, thus causing member 88 tocock so that the left end of arm 94 is lowered, the right end of arm 94maintaining its position against rod 140. As a result control rod 80 ismoved back into the body of pump 20 which decreases the displacement ofthe pump and thus slows down the wheel on the left side of the vehicleso that the vehicle turns toward the left.

Actuation of linkage 130 to move the rods 140 and 142 away from eachother permits the control rods 80 and 82 to move inwardly or outwardly,depending upon the bias imposed on T-shaped member 88 by fluid motor104. To increase the speed of the vehicle, movement of control rods 140and 142 toward or away from each other changes the speed ratio betweenengine 24 and the wheels, since the engine is the source of power fordriving the pumps and indirectly wheels 12 and 14; therefore, it may benecessary to accelerate the vehicle engine as linkage 130 is operated tomove rods 140 and 142 away from each other, to prevent the engine fromstalling, or to maintain adequate power at the wheels to drive thevehicle at the desired speed.

The mechanism may be modified to provide in effect an automatic drivetrain by adding a line 150 between valve 122 and pump 124 with arestriction 152 therein, and by utilizing a spring 154 connected to bellcrank 134 to bias linkage 130 to the position shown in FIG. 1 of thedrawings. With this modified system, the operator merely manipulatesvalve 122 to select either forward or reverse direction and thenaccelerates engine 24. The restriction 152, due to the variable outputof pump 124, provides a variable bias through fiuid motor 104 so that,as engine speed is increased, the bias on member 88 is increased anddcauses control rods 80 and 82 to move further inwardly or outwardly,thereby increasing the speed of the vehicle in a forward or reversedirection, in accordance with the power output of the engine.

While only one embodiment of the control system and one modificationthereof have been described herein, various other changes andmodifications may be made without departing from the scope of theinvention.

I claim:

1 A steering control system for a vehicle having a steering means and adual path hydrostatic drive with separate motors for two steerablewheels and separate variable output pumps for said motors: comprising ameans for controlling the output of each of said pumps, a longitudinalmember interconnecting said pump control means and being mounted forangular movement transversely of its longitudinal axis for operatingsaid control means, a linkage having two parallel members movable tovarious spaced relationships to one another for controlling the positionof the two ends of said longitudinal member and said pump control meansto control the output of said pumps relative to one another, means forurging said longitudinal member toward one of said parallel members toobtain forward travel of the vehicle and toward the other of saidparallel members to obtain rearward travel of the vehicle, means forconnecting said member to the steering means for varying the angularposition of said member on its transverse axis to vary the output of onepump relative to the other pump, and means for varying the spacingbetween said parallel members.

2. A steering control system for a vehicle as defined in claim 1 inwhich members connect the ends of said two parallel members to form aparallelogram.

3. A steering control system for a vehicle as defined in claim 2 inwhich a manually operated member is connected to one member of saidparallelogram to vary the spacing between said two parallel members.

4. A steering control system for a vehicle as defined in claim 3 inwhich said manually operated means consists of a foot-operated pedal.

5. A steering control system for a vehicle as defined in claim 1 inwhich a manually operated member moves said parallel members toward oneanother for controlling the output of the pumps relative to one another.

6. A steering control system for a vehicle as defined in claim 5 havinga steering wheel in which a member is connected angularly to saidlongitudinal member and a linkage connects said steering wheel with saidangularly positioned member for moving said bar to various angularpositions.

7. A steering control system for a vehicle as defined in claim 1 inwhich said means for urging said longitudinal member toward one or theother of said parallel members applies a yieldable force to said memberfor resiliently urging said member.

8. A steering control system for a vehicle as defined in claim 7 inwhich said means for urging said longitudinal member toward one or theother of said parallel members consists of a hydraulic motor and a valvefor controlling said motor to vary the direction of movement of saidmember toward one or the other of said spaced members.

9. A steering control system for a vehicle having a manual steeringmeans as defined in claim 8 in which a member is connected angularly tosaid longitudinal member and a linkage connects said steering means withsaid angularly positioned member for moving said member to variousangular positions.

10. A steering control system for a vehicle having a manual steeringmeans as defined in claim 1 in which a member is connected angularly tosaid longitudinal member and a linkage connects said steering means withsaid angularly positioned member for moving said bar to various angularpositions.

11. A steering control system for a vehicle as defined in claim 1 inwhich a member rigidly connected to said longitudinal member at rightangles connects said steering means to said member for urging one end orthe other of said longitudinal member toward one or the other of saidparallel members.

12. A steering control system for a vehicle as defined in claim 1 l inwhich said means for urging said longitudinal member toward one or theother of said parallel members consists of a hydraulic motor connectedto said right angle positioned member.

1. A steering control system for a vehicle having a steering means and adual path hydrostatic drive with separate motors for two steerablewheels and separate variable output pumps for said motors: comprising ameans for controlling the output of each of said pumps, a longitudinalmember interconnecting said pump control means and being mounted forangular movement transversely of its longitudinal axis for operatingsaid control means, a linkage having two parallel members movable tovarious spaced relationships to one another for controlling the positionof the two ends of said longitudinal member and said pump control meansto control the output of said pumps relative to one another, means forurging said longitudinal member toward one of said parallel members toobtain forward travel of the vehicle and toward the other of saidparallel members to obtain rearward travel of the vehicle, means forconnecting said member to the steering means for varying the angularposition of said member on its transverse axis to vary the output of onepump relative to the other pump, and means for varying the spacingbetween said parallel members.
 2. A steering control system for avehicle as defined in claim 1 in which members connect the ends of saidtwo parallel members to form a parallelogram.
 3. A steering controlsystem for a vehicle as defined in claim 2 in which a manually operatedmember is connected to one member of said parallelogram to vary thespacing between said two parallel members.
 4. A steering control systemfor a vehicle as defined in claim 3 in which said manually operatedmeans consists of a foot-operated pedal.
 5. A steering control systemfor a vehicle as defined in claim 1 in which a manually operated membermoves said parallel members toward one another for controlling theoutput of the pumps relative to one another.
 6. A steering controlsystem for a vehicle as defined in claim 5 having a steering wheel inwhich a member is connected angularly to said longitudinal member and alinkage connects said steering wheel with said angularly positionedmember for moving said bar to various angular positions.
 7. A steeringcontrol system for a vehicle as defined in claim 1 in which said meansfor urging said longitudinal member toward one or the other of saidparallel members applies a yieldable force to said member forresiliently urging said member.
 8. A steering control system for avehicle as defined in claim 7 in which said means for urging saidlongitudinal member toward one or the other of said parallel membersconsists of a hydraulic motor and a valve for cOntrolling said motor tovary the direction of movement of said member toward one or the other ofsaid spaced members.
 9. A steering control system for a vehicle having amanual steering means as defined in claim 8 in which a member isconnected angularly to said longitudinal member and a linkage connectssaid steering means with said angularly positioned member for movingsaid member to various angular positions.
 10. A steering control systemfor a vehicle having a manual steering means as defined in claim 1 inwhich a member is connected angularly to said longitudinal member and alinkage connects said steering means with said angularly positionedmember for moving said bar to various angular positions.
 11. A steeringcontrol system for a vehicle as defined in claim 1 in which a memberrigidly connected to said longitudinal member at right angles connectssaid steering means to said member for urging one end or the other ofsaid longitudinal member toward one or the other of said parallelmembers.
 12. A steering control system for a vehicle as defined in claim11 in which said means for urging said longitudinal member toward one orthe other of said parallel members consists of a hydraulic motorconnected to said right angle positioned member.